**6. Amphoteric character of halogen bonds**

The amphoteric character of halogen bonding was first proposed by Nelyubina et al. in 2010.[19] They were unable to find a true σ-hole in halogen bonds between I2 and I- . Rather, the I in both I2 and I had regions of electron density accumulation and depletion. When the I and I-I were interacting, both of them acted as donors and acceptors of electron density simultaneously. Nelyubina et al. defined this type of halogen bond as an 'amphoteric' interaction.
